The 30S ribosomal subunits of a number of acid-fast bacilli are found to be antigenic structures capable of eliciting delayed reactions in sensitized animals. They are both sensitive and specific skin test antigens. Studies will be done to determine if the 30S ribosomal subunits or any of the fractions obtained from attenuated Mycobacterium bovis (BCG) or M. tuberculosis (H37Ra) will elicit specific reactions in guinea pigs sensitized with homologous or heterologous organisms or with virulent M. bovis (Vallee) or M. tuberculosis (H37Rv). The study will then be extended to isolation of the various fractions from these virulent bacilli and testing these antigens in animals sensitized with the above organisms. The final phases of the study will be directed toward isolation of ribosomal subunits and fractions from other acid-fast organisms which produce disease in man and animals. These will include such organisms as M. balenei, M. kansasii and M. batteyi. The eventual aims of these studies are to provide easily produced skin test agents which are as affective as PPD and highly specific agents which will allow for specific diagnosis of illness or exposure to agents such as those discussed above. Protoplasm of acid-fast bacilli may provide material comparable to PPD, and 30S ribosomal subunits may provide the specific antigens.